1. Field of the Invention
The present invention relates to a linear image sensor device, and more particularly to a linear image sensor device with at least two line structures which can cover a wide dynamic range.
2. Description of the Related Art
A linear sensor is made such that its signal output varies linearly in relation to the quantity of the incident light. However, if the incident light quantity exceeds a given constant value, the signal output becomes constant, with the result that a sufficient signal output is unobtainable in the case of inputted information with a wide dynamic range. More specifically, if the incident exposure is set to match with a light portion of an object, the signal output taking place due to a dark portion thereof becomes small. On the contrary, if the incident exposure is set to match with the dark portion, the signal output due to the light portion comes into a saturated condition and assumes the same level. In other words, the dynamic range to the incidence of light is small.
For this reason, it is appropriate to provide a linear sensor device which does not show the linear relation between the incident light quantity and its signal output, for example, which has a logarithm characteristic. However, considerable technical difficulty is experienced to realize a linear sensor device with the logarithm characteristic, and hence it is not practicable. Thus, it has been desired to develop a linear sensor device having a wide dynamic range but being relatively low in the degree of technical difficulty.